The present invention relates generally to motor control and, more particularly, to a motor drive implementing a velocity noise filter to reduce noise susceptibility.
Rotating motors are typically controlled by a motor drive that receives a reference motor velocity signal and, based on the motor velocity signal, produces and outputs a torque signal that is applied to the motor. Adjustment of the torque signal based on changes to the reference motor velocity signal relative to the feedback motor velocity ensures that the motor rotates at the reference velocity.
Some applications require precise motor control across multiple, synchronized motors. For example, an electronic line system may be employed in a printing application to move the paper or other material over rollers and through various stages of the printing process. Typical printing processes employ multiple colors, each applied at different locations along the line. Hence, to ensure print quality, the various stages are synchronized. A lack of synchronicity between the stations results in misregistration between the colors, leading to unacceptable product that may need to be scrapped.
Previous generations of printing technology employed a mechanical line shaft mechanically linked to the various printing stations. Rotation of the line shaft by an electric motor activated rollers and printing stations along the line to conduct the printing process. In a mechanical line shaft system, factors such as play in the mechanical linkages, stretching of the paper web, and torsional flexing of the line shaft itself make it difficult to achieve and maintain synchronicity between the printing stations, especially during periods of acceleration and deceleration of the printing system. Typically, product generated during these periods is unacceptable.
More modern printing systems, commonly referred to shaftless printing systems or electronic line shaft systems, employ a plurality of motors and associated rollers that are electrically synchronized, as opposed to mechanically synchronized. Lack of synchronicity in an electronic line system results in similar problems, such as color misregistration, evident in a mechanical line shaft system.
When operating a plurality motors synchronously in an automated system, several factors exist that may cause the position of the motors to deviate from each other even though they are all operating under the same reference velocity signal. For instance, motor inertia and other losses at each motor are non-uniform, and could cause one motor to drift from the other motors.
Typical motor drives for controlling motors are implemented using software executed by a central processing unit (CPU). As CPU clock rates have risen, so too has the control bandwidth available to the motor drive. However, higher control bandwidth does not necessarily equate to higher performance. As bandwidth increases, so does the susceptibility of the motor drive to noise. Noise in this sense can generally be considered as rough operation, rattles, clunks, tendency to resonate, lack of robust performance, etc.
Typical physical processes in which drives are used cannot be effectively controlled at current bandwidth limits. The performance of a controller operating at such a bandwidth would be degraded by noise and overly aggressive control. Most processes have an ideal operational bandwidth that is much lower than the specified maximum bandwidth of the motor drive. For example, the operational bandwidth may be one or two orders of magnitude less than the theoretical bandwidth limit. If a motor drive is not effectively constrained, it has been observed that the drive can operate too aggressively, leading to less effective performance.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.